Electric heating element



March 23 T. w. GLYNN 2,673,142

I ELECTRIC HEATING ELEMENT' Filed April l5, 1949 'Fl G. l.'

JNVENTOR. THeoDoRE W. GLYNN A TTOR NE YS Patented Mar. 23, l1954 ELECTRIC HEATING ELEMENT Theodore W. Glynn, Kin to Blue Ridge Glass Tenn., a corporation of gsport, Tenn., assignor Corporation, Kingsport, New York Application April 15, 1949, Serial No. 87,754

4 Claims. 1

Heating elements made by the deposition of an electrically conducting grid on ceramic plates have the defect that the grid (generally of aluminum, silver, etc.) is subject to injury, thereby impairing the efficiency of the element and, furthermore, the grids unless protected by a second and non-conducting plate are liable to be shortcircuited or grounded. I

My invention has for its object a construction in which these objections are overcome. and to a method of applying and protecting the grid by which such improved heating elements may be more cheaply produced and for these ends consists in the feature hereinafter described and claimed.

Referring to the accompanying drawings in which similar parts are designated by similar marks of reference,

Figure 1 is a fragmental front view of a plate embodying my invention.

Figure 2 is a section on line 2-2 thereof.

The plate A may be of tempered glass coated with the selected conducting material B, say, aluminum, by a Schoop gun. Upon this uniform coating is impressed a design desired for the grid by placing over the coated plate a silk screen and applying thereto a medium having the characteristics set forth below. The medium passing through the silk screen imprints on the conducting coating the design of the grid. The plate with the medium thereon is then dried and baked at a temperature sufficient to harden and set the compound. The plate is then subjected to the action of a solvent capable of dissolving the conducting coating With which it may come in contact, but inert as to the baked medium. Thus, the deposited metallic coating is locally removed from the plate to leave the selected design for the grid thereon, all parts of the grid being covered by the hard and set medium C.

The medium to be used should have the following properties:

(a) Suitable viscosity and workability so that silk screen application is possible.

(b) After air drying or baking must be capable of protecting the aluminum coating from attack by the etching agent. The baking temperature should be as low as possible from the cost standpoint and cannot exceed the destraining temper ature of the glass.

(c) Must adhere rmly to the aluminum so it is not removed in the washing operation that follows the etching process.

(d) Since it is to be left in place on the heater plate, it must be capable of enduring the operating temperature of the plate indefinitely without deteration, discoloration, or oxidation, or change in electrical insulating properties.

(e) Must be odorless at the operating temperature of the plate.

(f) Must be an electrical insulator (g) Must be sufiiciently elastic so that it will not crack or peel off of the plate under repeated cycles of heating and cooling.

(h) Must have sufficient abrasion resistance so that it is not scraped or knocked oi the plate in ordinary handling operations before it is nally installed in the heating device.

(i) Must offer permanent protection to the aluminum against the attack of acids, alkalies and corrosive fumes which might be encountered in its final service as a heating device.

I find that these properties are found in the mixture of i Parts Silicone #996 varnish 860 Ground titanium dioxide 89o Ground silica 29 Lamp black 21 In this mixture the silicone varnish above referred to is one produced by the Dow-Corning Company and is a Well-known article of commerce. It is used as the vehicle for the other ingredients and is selected for that purpose because of its heat-resisting properties. The titanium dioxide and silica are llers and serve to stiften the varnish to fit it for the silk screen process. Neither detracts from the insulating properties of the baked compound. The lamp black serves to give color to the design and to thusrre'nder inspection easier. It also increases the radiation from the exposed surface of the grid and should not be used Where it is desired to suppress radiation from that side.

The plate with the design indicated thereon by the medium should then .be baked or cured at a, temperature of 250 C. for five minutes. The baking or curing temperature and time above given are subject to variation. It is only necessary that the medium is set sufliciently to withstand the action of the solution to be subsequently applied, the nal curing being eiected when the plate is put in use as a heater. Likewise they are affected by the grade used. If silicone #803 is used insteadof #996 the medium will air dry in 'about 16 hours and be ready for the solvent.

The solvent for the metallic coating is one tted to dissolve the latter at points to which It will be further found that the baked mediumv adhers closely to the metal on whichit is deposited, forming a non-conducting and hard coating, thus protecting the metali andipreventing short-circuit and grounding on4 accidental contacts.

What I claimy is: i

1. The hereinafter described method of making a heating element which comprises coating the surface of a ceramic` plate with a metallic conducting coating; printing on such coating:

through asilkscreena selected` design in. a medium comprising a silicone varnish and aller of non-conducting inorganic compounds of good heat stability, baking the plate with the design thereon and removingthe` exposed portionsof the metallic coating by a solvent inert to theprinting medium;`

2. The hereinafter described method of making a heating element which comprises coating the surface of a ceramic plate with a metallic conducting coating, printing on such coating through a silk screen a selecteddesign in a medium comprising a `silicone varnish anda filler of` non-conducting inorganic compounds of good heat stability, andlamp black, baking the plate with the design thereon,l and` removing the exposed portions ofthe metallic coating by a solvent inert to the printing medium.

3. The hereinafter described method of making a heating element which comprises coating the surface of a ceramic plate with a metallic conducting coating, printing on such coating through a silk screen a selected design in a medium comprising a silicone varnish and a filler of non-conducting inorganic compounds of good heat stability, drying the plate with the design thereon and-removing the exposed portions, of the metallic coating by a solvent inert to the printing medium.

4. The hereinafter described method of makingarheating element which comprises coating the surface of a ceramic plate with a metallic conducting coating, printing on such coating through'a `silkescreen a selected design in a medium comprising a silicone varnish and a filler offnon-conducting inorganic compounds of good heat stability, drying the plate with the design thereon sufiiciently to resist the solvent subsequently applied, removing exposed portions of the metallic coating by a solvent' inert tothe `printing mediumandthereafter drying and curingy saidmediumunder theheating effect cftheelectric current admitted to the metallic coating.v

THEODORE" W.l GLYNN,

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date `648,518 Ochs May 1, 1900 2,022,827 Ruben Dec. 3, 1935 2,081,894 Meyer i May 25,1937 2,460,795 Warrick Feb. 1, 1949A FOREIGN PATENTS Number Country i Date 101,011 Australia May 20, 1937 342,300 GreatBritain Jan. 28, 193,1 461,275 Great Britain Feb. 15, 193,7 

1. THE HEREINAFTER DESCRIBED METHOD OF MAKING A HEATING ELEMENT WHICH COMPRISES COATING THE SURFACE OF A CERAMIC PLATE WITH A METALLIC CONDUCTING COATING, PRINTING ON SUCH COATING THROUGH A SILK SCREEN A SELECTED DESIGN IN A MEDIUM COMPRISING A SILICONE VARNISH AND A FILLER OF NON-CONDUCTING INORGANIC COMPOUNDS OF GOOD HEAT STABILITY, BAKING THE PLATE WITH THE DESIGN THEREON AND REMOVING THE EXPOSED PORTIONS OF THE METALLIC COATING BY A SOLVENT INERT TO THE PRINTING MDEIUM. 